So-called boat leveling devices of the trim-tab type have been known for many years and various forms of them have been developed in an effort to maximize attitude control, stability of the marine craft and general hydrodynamic efficiency inclusive of decrease of flow velocity under the hull and fuel efficiency.
The prior art trim-tabs which typically are provided in pairs to enhance stability of the craft, is shown in FIGS. 1, 2, 3 and 4 herewith. More particularly, FIG. 1 shows a traditional external trim-tab 2.1 of which is attached directly to transom 3.1 of a craft 100.1 and in which the attitude of the trim-tab is controlled through a hydraulic piston assembly 4.1 which controls relative angulation of the hull relative to level of the water. Also shown in FIG. 1 is a servo-loop wiring 9.1 by which assembly 4.1 are controlled.
The prior art shown in FIG. 2 differs from that of FIG. 1 only in that the trim tab 2.2 is positioned beneath stern 6.2 of the craft 100.2 and forward of propeller 8.2. Therein, the direction of assembly 4.2 and hydraulic piston 5.2 are aligned with the gravity vector as opposed to the angled position of the hydraulic assembly shown in the prior art of FIG. 1.
The prior art shown in FIG. 3 demonstrates the hinge common in most trim tabs, that is, a pivot hinge 1.3 that fastens the planar surface 2.3 of the trim tab to the watercraft. The pivot hinge is fixed in a specific location, and requires an actuator 5.3, mounted at an non-right angle to allow the planar surface to descend.
The prior art shown in FIG. 4 shows a similar issue where the planar surface 2.4 is fastened directly to the hull of the watercraft by a living hinge 7.4. This living hinge 7.4 is in a fixed location as well, and thus requires an actuator 5.4 mounted at a non-right angle, or the actuator 5.4 with a pivot mount to allow the planar surface 2.4 of the trim tab to descend.
In general trim-tabs of the prior art, whether double or single acting, will operate upon the same principles and have a common objective, namely, that of contributing to the efficiency control of the boat's attitude, stabilization and general hydrodynamics.
There are significant differences between the prior art and the current invention. Primarily, the use of a living hinge as in the prior art of Arnseson U.S. Pat. No. 4,909,175 and Weiler, U.S. Pat. No. 3,463,109, do not allow an extent of slidability for the trim tabs it connects. Arnseson uses a living hinge 7.4, which is a thin flexible hinge made from the same material as the two rigid pieces it connects. Weiler uses a pivot hinge 1.3, which allows its trim tab 2.3 to raise and lower, but is limited to pivoting around its connection point. Thus, there exists a need for a fluid-hinge to allow slidability of the trim tab it connects.
In recent years, most efforts of the prior art have been directed primary to improvement of the electronics and the development of algorithms to optimize trim-tab control under various conditions of vehicle speed, wave conditions, shape of the boat's hull, having distribution in craft, and other hydrodynamic considerations. The prior art also has experimented with the efficiency of electric motor controls of the trim tabs as opposed to that of the hydraulic systems shown in FIGS. 1 and 2. In general, the durability of electric motor controls have proven to be superior than that of hydraulic actuators.
The U.S. Navy has undertaken significant research and development in this area to attempt to maximize performance of a variety of its boats and, typically, of the types employed by the U.S. Coast Guard. In Navy terminology, a trim-tab is referred to as a stern flap, apparently because its engineering objectives are more ambitious than are the case with a leisure class powerboat. More particularly, the Navy has identified the following criteria as hydrodynamic mechanisms which account for improved boat performance based on optimized stern flap design.
After Body Flow Modifications:                Flow velocity under the hull decreased.        Pressure recovery increased.        Transom exit velocity increased.        
Wave System Modifications:                Localized transom system wave system altered.        Near field wave heights reduced.        Far field wave energy reduced.        
Secondary Stern Flap Hydrodynamic Effects:                Ship length increased.        Beneficial propulsion interactions.        Ship trim modified (bow down trim induced).        Ship sinkage is reduced.        Lift and drag forces developed on flap.        
The within inventor has recognized that the fundamental objectives and benefits of trim tabs and stern flaps may be more effectively achieved if the entire length of the trim-tabs or stern flaps are extended. And that, when properly actuated and controlled, such elongated attitude control element, as suggested can accomplish and substantially improve upon the performance of prior art trim tabs and stern flaps regardless of hydrodynamic conditions. The efficiency of the present invention may be yet further improved the assistance of contemporary electronic controls and algorithms. The present invention also improves upon efforts that seek to improve the performance of trim tabs thereof through modification of their geometry as, for example, is reflected in U.S. Design Pat. No. 292,392 (1987) to Zepp, entitled Boat Leveler Twin Tab; U.S. Pat. No. 6,038,995 (2000) to Karafiath et. al, entitled Combined Wedge-Flap; and U.S. Pat. No. 3,092,062 (1963) to Savitsky entitled Mechanical Control for Submerged Hydrofoil Systems.